The present disclosure relates to providing protection for ink printing on sheet media, both on electrostatically printed sheets and on ink jet printed sheets in a photocopier/printer.
Heretofore, it has been desired to provide a fixative coating over the ink printing on the sheets discharged from digital printing on a print engine, particularly colored ink printing, to preserve the ink marking and prevent smudging or other damage to the inked surface of the print media. For example, it has been desired to protect the printing from abrasion in the transport of the printed sheets from the print engine. Attempts to protect the surface of ink printed media have attempted the use of aqueous flexovarnishing; however, the high water content of such aqueous mixtures have required substantial amounts of drying, thereby increasing the size and cost of the equipment and has delayed the speed of transport rendering the process unworkable for high speed printing applications.
The problem of providing a protective coating for inked print media has further been complicated by the need to accommodate print media of both plain paper and coated paper sheet stock in widespread use in digital print engines.
Known processes for applying an aqueous flexovarnish coating on inked print media have required relatively long equipment modules with prohibitively large space requirement and thus have not been practical for many digital printing installations. Furthermore, the requirement for changing the flexible plates and the necessity of cleanup operations each time the sheet format is changed have rendered such a process cumbersome and prohibitive for small print engine installations.
Thus, it has been desired to provide a way of applying a transparent protective coating to inked print media in digital printing operations in a manner which does not require large equipment installations and does not require a reduction in the speed of the copying/printing operation.